Kinesiology of the empty can test.

The "empty can test" has been described to isolate supraspinatus muscle activity from the activity of other rotator cuff muscles. The shoulder is positioned in 90 degrees of abduction, with full internal rotation, and 30 degrees of forward flexion and maintained against resistance. The purpose of this study was to determine if the supraspinatus muscle is isolated by the empty can test. Ten normal male subjects were studied (age 25-43/mean 32) with fine-wire electromyography recording from their nondominant arm middle deltoid, supraspinatus, infraspinatus, and teres minor. During the maneuver electromyogram activity was seen not only in the supraspinatus, but also in the infraspinatus and the middle head of the deltoid. Teres minor was inactive throughout the test; however, this is interesting because the teres minor and infraspinatus have previously been described as a functional unit. Our study found that the empty can test does not allow selective activation of the supraspinatus muscle.